The MRI apparatus is an apparatus that measures an NMR signal generated by the object, especially, the nuclear spins of atoms which form human tissue, and images the shapes or functions of the head, abdomen, limbs, and the like in a two-dimensional manner or in a three-dimensional manner. In the imaging, different phase encoding and different frequency encoding are given to NMR signals according to the gradient magnetic field, and the NMR signals are measured as time series data.
The measured NMR signals are temporarily arranged in measurement space called k space and reconstructed as an image by a two-dimensional or three-dimensional Fourier transform. In this case, when echo signals of different TE (echo time) are arranged in the k space so as to be adjacent to each other, the quality of a reconstructed image is degraded due to the characteristics of the reconstruction method. In addition, in the k space, when a TE difference between adjacent echo signals is within a predetermined range, the echo arrangement is said to be continuous.
There are various imaging methods. For example, there is multi-echo imaging in which a plurality of NMR (echo) signals (echo trains) are collected during 1 TR (repetition time) to fill the k space after one excitation pulse (90° pulse) application. In the multi-echo imaging, a plurality of regions of the k space can be filled by one excitation pulse application. In such multi-echo imaging, the echo arrangement has been studied in various ways in order to obtain a desired contrast image while maintaining the continuity of the echo arrangement (for example, refer to PTL 1 and NPL 1).
In addition, there is multi-echo multi-contrast imaging in which a plurality of k spaces are filled using a plurality of echo signals, which are collected by the multi-echo imaging, to reconstruct a plurality of different contrast images. Such multi-echo multi-contrast imaging can be accelerated by sharing (echo sharing) some of the filled echo signals between the k spaces (for example, refer to PTL 2).